Monitoring and controlling circuits for program distribution



Sept. 18, 1928.

J. F. TOOMEY MONITORING AND CONTROLLING CIRCUITS FOR PROGRAM DISTRIBUTION 3 Sheets-Sheet Filed July 31, 1924 .EIIQ

INVENTOR ATTORNEY Sept. 18, 1928.

J. F. TOOMEY MONITORING AND CONTROLLING CIRCUITS FOR PROGRAM DISTRIBUTION Filed July 31, 1924 3 Sheets-Sheet q INVENTOR J}? YEW/nay A TTORNE Y Sept. 18, 1928.

J. F. TOOMEY MONITORING AND CONTROLLING CIRCUITS FOR PROGRAM DISTRIBUTION Filed y 31, 1924 5 Sheets-Sheet INVESTOR .[F JZYW/N/ A T ORNE Y Pasta Sept. 18, 1 928.

- UNITED "STATES JOHEN r. TOOM-EY, ornnw Yonx, N. Y., AssIouon 'ro AMERICAN rnra'rnonn rnnnoaarn oourAmr, A CORPORATION or NEW YORK.

PATH

OFFICE.

AND

MONITORING AIWD CONTROLIJING CIRCUITS FOR PROGRAM DISTRIBUTION. i

- Application filed July 81,

. This invention relates to transmission sys-. tems and more particularly to monitoring and controlling arrangements for such systems.

In a system for the transmission of programs over wires, it is proposed to extend trunks from the main studio to central oflices or distributing points. At each central oflice rality of branches extending to local sub scribers provided with loud speakers or head receivers. 1

In a system of the type above described, it is essential that the attendant atthe main studio have some means'of knowing that the operation of the various parts of the system, as well as the system as a whole, is satifaotory. It is, therefore, one of the purposes of the present invention to provide monitoring Y and control circuits to enable the studio attendant to easily and quickly determinewhich parallel the trunk carrying the program to the centraloflice and which is extended as a common circuit to each apartment house equipment ,1 I

Among other advantages, the arrangements of the present invention permitthe 'studioattendant to monitor on the output of any amplifier, that is, either the main amplifier at the central oflice or the individual amplifiers at the difierent apartment houses or at other central oflices. The studio attendant is also enabled to adjust the output of the main amplifier at the central oflice. Furthermore, the studio attendant may call the central oflice attendant on the telephone when required, and the central oflice attendant mayv likewise call the studio directly if desired.

In accordance with the present invention it is also proposed to provide visualor audible signals at the studio which indicate that the system is functioning properly, that, is,

, when all the amplifier'and power equipment 1924. stra n. v aasve,

an operativecondition.- In caseany of this equipment fails, the signaling system indicates thls fact. Itis preferred to transmit tween the studio and central oifice, leaving the program trunk free of all other apparatus other than that required for transmitting the program. Between the central oflice and the apartment houses, however, the signals may be sent over the trunk carrying the program.

' The invention may now be more fully understood from the following description when read in connection with the accompan ing drawing, Figures 1, 2 and 3 of which, when placed end to end, illustrate the pre ferred embodiment of the invention.

Referring to the drawing, PT designates a 'main trunk extendingfrom the studio at the all of the signals over' the control circuit bemain station to a central otfice provided with amplifying equipment, as indicated at A and A 1n Fig. 2. Bus-bars 10 are connected to the output side of the amplifiers A and A and f to these bus-bars a plurality of trunks, such as PT are connected, each-trunk leading to r an outlying apartment house or other local distributing point. At each apartment house, amplifying equipment, as indicated at A and in Fig. 3 is provided. Bus-bars 11 are connected to the. output side of the amplifier at the apartment house and distributing circuits leading to each subscriber s station may be connected to such bus-bars.

V In order that the studio j attendant may monitor on'the various trunks to determine the quality and volume of transmission being received at variouspoi'nts, a monitoring circuit MG isprovided, as shown Fig. 1,

which maybe plugged by means of a plug P into jack J of a monitoring trunk MT, ex-

tending from the studio to the central olfice, at which point the trunk may be switched under the control of the attendant at the studio either to the output bus-bars of the amplifier A at the central oflice, over the conductors 12,. or to an auxiliary monitoring trunk MT having branches which may be connected to the output bus-bars of the amplifier at any apartment house, the connection of these branches being controlledfrom the studio.

'- In order to control the switching of the monitoring trunks to the output bus-bars of the various amplifiers, the studio attendant is provided with a dial 13 by means of which impulses maybe transmitted to operate stepby-step switches SW and SW. The switch SW controls theestablishment of connections over conductor 14 and over conductor 15,

from the monitoring trunk to the output busbars of any amplifier either at a central office or at an apartment house. The switch SW may selectively operated to adjust the potentiometer P0, associated with the input side of the amplifier A at'the central office init the central office a spareamplifier SA may be provided so that if the amplifying equipment A-'A' is not functionin properly the spare amplifier ma be su stituted therefor under the control of the switchlS-W.

A telephone set 14 is provided for the use of an attendant at the central ofiicerand-"by sending a proper code by means of'the dial 13 the studio attendant may actuate the switch SW to connect thecentral oflice attendantsset to the trunk MT, thereby enabling the two attendants to converse with each other.

Further details of the apparatus will be clear from a description of the operation thereof, which is as follows: When the attendant at the studio desires to start the program, the program trunk PT is connected to the studio transmitting apparatus by means of the Jack PJ, and the key K associated with the monitoring trunk MT is actuated. A circuit is closed by the key K from battery V through marginal relay S over the inner right-hand normal contact of the relay S, contact of the key K, midpoint of retardation coil RC, thence over thetwo sides I of the trunk MT, midpoint of the retardation coil RC and thence through the winding of the marginal relay PM and the high resistance wiirding of the relay S to ground. Relay S is marginal and does not receive sufficient current in series with the high resistance winding of the relay S to operate. Relay PM is also marginal andonly operates in series with the high voltage battery V as will be described later. The relay S is energized, however, and completes a circuit from ground, over its front contact, through the winding of the relay S and through the winding of the relay S to battery. Relay 8,, upon being energized, performs no useful function at this time but relay S completes a circuit from ground, over its front contact,

throggh the winding of relay V to bat tery At its left-hand front contact, relay V establishes a circuit for the filaments of the amplifiers A and A from battery V over the left-hand front contact of relay V, through resistance 15 and through the filaments of the tubes' 16, 17 and 18 in series to round. As soon as the filaments of the tu es glow, plate current from the 350 volt source is supplied through the choke coil 19, through the winding of relay Y tothe plates of the tubes 16 and 17 and from the coke coil 19 through the resistance 20 and the winding of the relay I to the plate of the tube 18. If the 350 volt source is a normally operative source, the space current at once begins to flow through the relays I and Y. If, however, the 350 volt source is a generator, the outer ri ht-hand front contact of the relay V may e arranged/t0 start the generator in a manner well known in the art, so that as soon as the generator gets up speed and generates the desired volt age, the current will flow through the relays I and Y to energize their windings. As soonrelay S and over conductor 22 to a contact controlled by the rela G in Fig 3. This circuit will be complete upon the energlzation of the relay C in a manner to be descrlbed later. 1

Returning to the relay V, battery V is connected over its inner right-hand front contact to the auxiliary bus-bar 23, associated with the trunk bus-bars 10, so that current flows over the conductor 24, over the back contact of relay 0,, through the winding of marginal relay 0, to the midpoint of the retard coil RC over the two sides of the trunk PT to the midpoint of the retard coil RC,

and thence through the high resistance wind-,

ing of the relay G and through the winding of he marginal relay C to ground. Relay C is marginal and does not receive sufficient current in series with the high resistance winding of relay C to be' energized. Relay C, is also marginal and only operates when its circuit is connected to the high voltage source V as will be described later. Relay C, is energized, however, and completes a circuit from ground, over its front contact, through the winding of relay C to battery. Relay 0,, at its right-hand front contact, connects battery through the resistance 23, choke coil 24,'through the filaments of tubes 25, 26 and 27 in series to ground. As in the case I of the amplifying equipment at the central oifice in Fig. 2, the 350 volt plate source may be a dynamo machine, in which case the lefthand contact of the relay C, may close a circuit to start the dynamo machine in a Well known manner.- As soon as the space current flows through the tubes, the relays I and L will be energized to complete a circuit from ground, over the front contact of the relay L, front contact of relay I, through the lefthand winding of the relay H to battery. Re-v lay H is then locked up over its right-hand front contact and over the front contact of relay C to ground.

"tive condition so that the through the left-hand locking contact anding of the relay At its outer left-hand front contact relay H completes a shunt path'through the low resistance winding of relay C, over the outer left-hand. front contact of the relay H back contact of relay 0,, to the terminal of "the winding 0,, this shunt path being in shunt with the high resistance winding. of the rela (1,. The current is increased throu h the winding of the relay C, but is still insu cient to energize said winding. The increase in the current flow over the circuit is suflicient, however, to operate the marginal relay G which completes a circuit from ground, over its front contact and over the similar contacts of other relays corresponding to C and associated with other trunks, and thence through the winding of the relay 0 to battery. It will be understood that the contacts of the relays corresponding to C, of other trunks associated with the bus-bars 10 will be energized-ip/aomanner similar to that described in connection with the circuits associated with the trunk PT,.

Upon the relay C attracting its armature, ground is connected to the conductor 22, thereby establishing a path'through the low resistance shunt winding of relay S, (see Fig. 1) from "round, over the front contact of the relay hand back contact of-relay S over conductor S and throu h the low resistance wind- 2 in parallel with its high resistance winding to the terminal of the marginal relay PM. The current is increased through the marginal relay PM but is insulficient to actuate said relay. The increase in the flow of current over the circuit including therelays PM and S however, is sufiicient to energize the marginal relay S which attracts 1ts armature and closes the circuit from ound, over its front contact. and throu Ii the winding of the relay X. The relay at its ri ht-hand front contact, completes a circuit rom ground over the back contact of relay Y, over the front contact of relay X and through-the O. K. signal lamp 28. The glowing of the O. K. lamp indicates that all of the apparatus is in normal operaprogram may proceed.

If the filament of either tube 16 or tube 17 at the central oflice should burn out, the de-- crease or'interruption, as the case may be, of

the space current through the relay Y will cause said relay to be deenergized and a circuit will then be completed from ground, over the front contact of the relay S (see Fig. 1), over conductor 14, over the front contact of relay I,back contact of relay Y,

locking winding of the relay S through the winding of the relay S to battery. The

(I, over conductor 22, over the front right-hand contact of relay S rightrelay S upon being deenergized, at its left- I to noti At its right-hand contactrelay S opens the shunt circuit through the low resistance winding of the relay b previously traced over conductor 21. This causes the marginal re-- 'lay S to be deenergized, thereby completing a circuit from battery,'-through the winding of the relay-X and .over its'left-hand locking contact, over the contact of the restored key 30, and through the winding of relay Y to ground. Relay Y is now locked :up in series with the relay X and at its innerright-hand contact opens the circuit of the O. K. signal hand contact closes the circuit of the bell 34; 1 the attendant at the central otfice. i

28, and at its outer right-hand front contact completes a circuit through the alarm signal 31 and the relay 32. The relay 32 closes a circuitof the bell 33 so that an audible as well as a visual signal is given at the studio.

- If the filament of the tube 18 at the central oflice should burn out the relay I would be released. If the 350 volt power source should fail, both relays I and Y would be released. In either case a circuit would be completed from ground to conductor '14, over the back through the winding of relay S to battery. Relay. S would thus be energized with the same results as previously described.

' If the filament of the tube 27 at the apartment house should burn out, the space current would. be interrupted s'othat the relay I would release its armature and close a circult from ground, over the front contact of relay L,-back contact of relay .1, over the inner Relay 0,, upon being energized, opens the low resistance shunt through the low resistance winding of the relay C thereby decreas mg the current flow through the marginal relay- C, and causing said relay to release its armature. Relay 0, opens a circuit of the relay 0, which in turn disconnectsground from conductor 2 and'thereby opens the low resistance shunt circuit through the low resi'stancc winding of the relay 8,, thereby causin a decrease in current through the contact of relay I, over the left-hand locking contact and locking winding of relay S relay -(see Fig. 1"), causing said relay S to release and give'the alarm signal, as pre viously-described. 1

Upon receiving the alarm signal, an attendant may be sent to repair the difficulty in the usual manner. in connection with the amplifier at the apartment house, the relay C, would be released as soon as the relays I and L are again energized, thereby again closingthe low resistance shunt through the low resistance winding of the relay 0,. This in turn closes the shunt circuit previously traced through the low resistance winding of the relay S (see Fig. 1) and causes the marginal relays S to be again energized. The energization of the relay S at once short circuits the winding of the relay Y, which is released to open the alarm circuit and close the circuit of the O. K. signal 28. In case the trouble arose in connection with the amplifier at the central oifice, relays I and Y will again be energized as soon as the trouble is repaired, thereby opening the circuit of the relay S and in turn closing the low resistance shunt through the low resistance winding of the relay S Relay S is then again energized with the same results,

as already stated.

' When the studio attendant wishes to discontinue the program, the key K is restored, thereby releasing relay S Relay S in turn opens the circuit of relay S which disconnects ground from the relay V associated with the central office amplifier. Relay V, upon releasing, at its left-hand contact opens the filament circuit of the amplifiers A and A, causing relays I and Y to be deenergized and relay S to be restored to normal.v Relay V, at its right-hand contact, disconnects ground from the bus-bar 23, thereby opening the circuit of the relays corresponding to (L and C of all the trunks, such as PT Relay C is released, thereby restoring the relays C, and H to normal. Relay C disconnects battery from the filament supply circuit of the amplifiers A, and A',, thus bringing all apparatus to its normal condition.

When the attendant at the studio wishes to monitor on the output. of the central oflice amplifier, he inserts the plug P of the monitoring circuit MC in the jack J of the monitoring trunk MT. The insertion of the plug P closes the circuit of the relay S. The relay S at its inner right-hand front contact disconnects the relay S from the circuit previ-.

ously traced over the key K (which is closed as previously described in order to render all of the apparatus operative) and connects the circuit over the key K from the inner righthand front contact ofrelay S, over the sleeve conductors of the jack J and plug P, through the resistance 35' of the dial 13, over the normal contact of the dial 13, over the contact of the release key 36, to battery V The battery V is a high voltage battery but the resistance- 35 is so proportioned as to maintain thesame current flowing through the relays PM and S at the central oifice as that In case the trouble arose obtained with the battery B Therelay S, therefore remains in operative condition.

The attendant at the studio then operates the. dial 13 to send a proper number of impulses to operate the switches SW and SW to the desired point, which in this case we will assume to be the sixth point of the switch. As soon as the dial is operated to the OE normal position, the off normal contacts of the dial short circuit the resistance 35, thereby permitting additional current to flow to operate the marginal relay PM as well as the relay S As the dial returns to normal, impulses are sent over the circuit including the relays PM and S by interrupting the circuit through the impulse contact of the dial. As soon as the relay PM was energized, as originally described, it closes a circuit through the stepping magnet SM and through the slow release relay SR at its front contact. The slow release relay SR holds open the circuit which extends over the back leasing, remains energized during the inter ruptions of its circuit each time the armature of the relay PM falls off in response to the transmission 0 an open circuit impulse. This prevents ground being connected to the arm of the switch SW or switch SW, as the case may be, during the momentary intervals that the armature of the relay PM is on its back contact.

The impulses transmitted through the stepping magnet SM advance the wipers of the switches SW and SW to the sixth contacts of each switch. The relay S at its outer armature controls the connection from the back contact of the relay PM to the arms of said switches. When the-relay S is deener gized, the arm of the switch SW is disconnected from the circuit and the arm of the switch SW is made effective. When the relay S is energized, the connections to the switch wipers are reversed, the wiper switch SW being disconnected and the wiper switch SW being rendered effective. As soon as the dial 13 has reached its normal condition, the short circuit about the resistance '35 is removed so that the current flowing through the relays PM and S is reduced sufliciently to deenergize the relay PM. The slow releasemela SR, which prevented the closing of a circult to the wipers of either switch SW .or SW, after a moment releases its armature,

thereby completing a circuit from ground, over the back contact of the relay PM, back contact of relay SR, back contact of relay RM, outer ri ht-hand back contact of relay S over the w iper of the switch .SW and the sixth contact of the switch SW, through the winding of the relay S to battery. Relay S upon being energized, disconnects the trunk MT from the trunk MT and connects the trunk MT over the conductors 12 to the contact of the relay RM tothe outer armature of therelay S The relay SR, being slow re:

4/ output bus-bars of the amplifiers A A.

. of the circuit over the controlling key The studio attendant can now listen to the output circuit of the amplifying e uipment at the central station by means 0 his receiver, which is connected across the m'oni': toring circuit. I

Assuming now that the studio attendant wishes to monitor on the output of one of the apartment house amplifiers, he must first restore the switches SW and SW to normal position, for these Switches when once ad vanced remain in their advanced position until restored by some special action. The res toration of the switches may be accomplished by either momentarily removing the plug P from the jackJ or by momentarily operating the release key 36. Momentaril withdrawing the lug causes a momentary interru' tion operations, therefore, causes a momentary release of the relay S Belay S however, being a slow release relay, is not released under these conditions and maintains the ground connection to the conductor 14 so that the amplifying. equipment remains in operative condition. Relay S being a quick release relay, opens its contact but performs no useful function at this time.

Relay S is momentarily released, thus momentarily connecting ground over its back contact, over the OE normal contact 37 (which was closed as soon as the switches. SW and SW moved off normal). and through the winding of the release magnet RM to battery. The release magnet restores the switches SW and SW to normal. A contact is rovided on the release ma et RM which ho 'lds 0 en the circuit to the rushes while the switc es are being restored to normal.

In order to monitor on one ofthe apartment house amplifiers, for example, the amplifiers A and A,, the attendant, after restoring the switches to normal, as above described, will then dial the roper code number, which is assumed to e 3, to step-the switches SW and SW around to the third terminal. The third terminal of the switch SW is connected over conductor 38, through the winding of the relay 0, to battery V (see Fig. 3). The switches SW and SW are advanced in the manner previously described by the operation of the dial, and the relay S, not being energized, a circuit will be completed at the close of the dialing operation from ground, over the back contact of the relay PM, back contact of relays SR and RM, outer back contact of relay S wiper of the 'tendantis now enabled'to listen for switch'SW, thirdcontact of switch SW, over the conductor 38 and through the winding of.

the'relay Q, to battery. Relay G u on opcrating, disconnects the circuit throng relay .0, and the retard coils associated with the trunk PT from the battery connection over the conductor 14, and over the inner righthandfront contact of relay V to the battery V and substitutes a-direct connection to the high potential battery V Therefo re the current through the circuit of relays (1, C,

and C is now sufficiently increased to operate the marginal relay C Relay (L closes a circuit of the relay C and connects the monitoring trunk MT to thebus-bars of the amplifying equilpment A and A at theapart ment house s own in Fig. 3. The stud o at on the output circuit of this amplifier.

It should be noted that the monitoring and 7 control circuit MT is common to all of the apartment house amplifiers that are fed from the amplifymg'e uipment A-A at the central ofiice, so that y dialing the proper numher the attendant at the "studio can monitor on the amplifierat the central ofiice or on any apartment house amplifier connected to the central oflice amplifier. 4

When the studio attendant is through monitoring on the circuit, the switch at the' central ofiice is resorted to normal either by means of the release key 36 or by removing a the plug P from the jack'J, as already'described. Let us assume now' that the studio attendant has dialed the proper number to advance the wiper of the switch SW to its sixth contact so that the attendant is monitoring on the output circuit of the central oflice amplifier equipment. A and A, and that the attendant wishes to increase or decrease the volume of'the'output of the amplifien' In this case, the switches SW and SW are restored to normal as before and the attendant dials a code number, which will be assumed to be 9. The operation of the dial will therefore advance the wiper of the switch SWto its 7 ninth contact, which is connected to the winding of the'relay S, (the wiper of the switch SW is, of course, advanced at the same time but is without eflect because the relay S is deenergized). As soon as the dial returns'to normal, the ground fplaced upon the circuit by the back contact 0 a circuit of the relay S At its right-hand contact, relay S, disconnects ground from the relays S to S inclusive, which may have been previously locked up, and at its righthand front contact rela S completes a circuit through the rightand winding of the relay 8,. S is locked upthrough it's righthand'winding and over its inner right-hand front contact,'and over the front contact of relays S andS, to ground. The action of the relay Spis only momentary for it comthe relay PM completes m conductor 39, thereby releasing any of the pletes a circuit at its left-hand front contact,

over the 'ofi nor'malcont'act 37 over there lease ma net RM of the switches, thereby reswitches SW and SW aroundto the proper contact to close the circuit of'one of the potentiometer controlling relays S,,, S or. S Assuming the code number transmitted 1s 9, the brush of the switch SW Wlll be advanced I to its ninth contact and as soon as thedial is restored to normal, ground is connected over the back contact of the relay PM 'to the outer armature of the relay S as before, and thence over the outer front contact of said relay S over the wiper of the switch SW, and. over conductor 40,'through the upper winding of the relay S to battery. Relay S 1s energized and locks up through its lower winding and over'its lower front contact to grounded conductor 39. The relay- S upon being energized, connects the input winding of the amplifier A to the outer connections of the potentiometer P0.

The studio attendant may now operate the release key- 36 and restore the switches SW and SW to normal.- The momentary release of the relay S unlocks the relay S so that it is also restored to normal- The attendant rmay now dialthe proper code number to enable him to monitor on the output of the.

amplifier A and determine if the setting of the potentiometer is proper.

It will be apparent that in a similarjmagnner the attendant may, by dialing the proper number of impulses the second time, complete circuits for either of the'relays S or S and cause other settings in the potentiometer. The first dialing operation in each instance energizes the relay S to unlock any of the relays S S or S previously. locked'up before the final set of impulses is transmltted. It will also be apparent that at any time the attendant may release any of said relays and leave the potentiometer in its normal setting, as indicated in the drawing, merely by dialing nine impulses to operate the relay S which disconnects ground from conductor. 39; The switches, after being thus advanced, are automatically restored to normal, as previously described, but it will be necessary to operate the release key 36 or momentarily disconnect the plu P from the jack J in order to unlock the re ay S 1 v If the studio attendant should desire to substitute the spare amplifier SA for the am-.

plifying equipment A-.A at the central office, the attendant will first operate the dial to send nine impulses, thereby advancing the the relay. S, to lock up the relay S The switches are automatically restored to normal, as already described, whereupon the attendant dials the second setof impulses to advance the brushes of the switches SW and SW to their fifth contacts. As soon as the dial is restored to normal, relay PM connects ground over its back contact to the conductor connected to the outer right-hand armature of locked-up relay S so that ground is connected over. said'armature, over the outer front contact of said relay, over the wiper of the switch SW, fifth contact of switch SW, conductor 41, through the-winding of relays S and S in series, and thence to battery. Relays S and S disconnect the amplifiers A-A and substitute therefor the spare amplifier SA. Relays S and S are (locked 11 over the lowermost front contact of 'relay and over conductor 39 to ground,

desire to release these relays and. again connect the amplifiers A and A" to the circuit, it

is only 'necesssary to again dial 9, thereby advancing the swltch SW to its ninth contact and closin the circuit ofrelay S which momentari y removes ground from conductor 39 and unlocks the relays S, and S The switches are'automatically restored to nor mal by a circuit closedover the left-hand front contact of relay S as previously descr1bed,fand the relay S may be released by momentarily actuating the release key 36;

In case the studio attendant .wishes to call the central office attendant on the telephone, the plu P of the monitoring circuit MO is inserte in the jack J, as already described,

and the dial is operated to send the proper code, which in-the case assumed is 7. The wiper of the switch SW is advanced to its seventh contact, which is connected over conductor 42 through the winding of the relay S to battery. Upon this relay being select ed, it is energized and connects the central otfice operators set 14 to the trunk MT, WlllCh in turn is normally connected to the trunk MT. At its lowermost front contact relay S completes a circuit over the normal swltchhook contact of theset 14;,- through the buzzer or call bell'BZ', thereby notifying the centralpflice operator that he is wanted. After I with the central oflice attendant, the stujio attendanu-by removing the plug from the jack, will automatically release the switches SW and SW and release the relay-S thereby disconnecting the central oflice subscribers telephone from the monitoring circuit. V

If the attendant at the central oflice wishes to communicate with the studio attendant, the key K at the central office may be closed,

' thereby energizing the relay 8,, and connecting the operators set to the trunk MT, as already described. The attendant may then operate the ringing key K, to connect ringing current'to the trunk. This actuates the drop 43 at the studio so that the studio attendant may plug his set into the jack J and answer the call. At the close of the conversation the central ofiice operator will release the key K and disconnect his set, the central oflioe operator disconnecting his set by'withdrawing the plug P from the jack J.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the appended claims.

What is claimed is: .1

' 1. In a signaling system, a transmission circuit extending between two stations, means to impress signals upon said circuit at one of.

said stations, an auxiliary monitoring circuit extending between said stations, an attendants monitoring setat said first station, and means at said second station controllable by the attendant at said first station, to connect said monitoring circuit to the terminals of said first mentioned circuit at said second station to enable the attendant to monitor the transmission of signals from said first to said second station.

2. In a signaling system, a transmission circuit extending between two stations, means to apply signaling currents to said circuit at one station, amplifying equipment associated with said circuit at the other station, an auxiliary monitoring circuit extending between said stations, an attendants monitoring set associated with said monitoring circuit at said first station, and means at said second station controllable by the attendant at said first station to connect said auxiliary circuit to the output side of said amplifying equipment at said second station .to enable the attendant to monitor on the output of said amplifying equipment.

3-. In a signaling system, a transmission trunk extending from a transmitting station to a central oifice, branch trunks extending from said central oflice to outlying points, a monitoring trunk extendin from said transmitting station, and means or selectively connecting said monitoring trunk to said main trunk at said central otfice or to any one of said branch trunks at said outlying points;

4. In a signaling system, a main transmis: sion trunk extending from a transmitting station to a central office, amplifying equipment associated with" said said central oiiice, branch trunks extending from said central ofiice to outlying points, amplifying equipment associated with each branch trunk at each outlying point, an auxiliary monitoring trunk extending from said transmitting station, and means for selectively connecting said auxiliary trunk to the outputof said amplifying equipment at the central ofiice or to the output of any amplifying equipment at any of said outlying points. 7

5. In a signaling system, a main trans mission trunk extending from a signaling station to a central otfice, amplifying equipment associated with said trunk atsaid central ofiice, branch trunks extending from said central oilice to outlying points, amplifying equipment associated with each branch trunk at each outlying point, an auxiliary. monitoring'trunk extending from said signaling station, and means controllable by an attendant at said signaling station for selectively connecting said monitoring trunk to the output of any amplifying equipment in the system.

6. In a signaling system, a main transmission trunk. extending from a transmitting station to a central oflice, ,amplifying equipment at said central oflice, branch trunks extending from said central oflice to outlying points, amplifying equipment associated with each branch trunk at each outlyingpoint, an auxiliary monitoring trlmk extending from said transmitting station, and selective switching means controllable by an attendant at said transmitting station for selec tively connecting said monitoring trunk to the output of any amplifying equipment in the system. 7. In a signaling system, a main transmission trunk extending from a transmitting station to a central oflice, amplifying equipment associated with said trunk at the central oflioe, branch trunks extending from said central oifice to outlying points, amplifying equipment associated with each branch trunk at each outlying point, an auxiliary monitor ing trunk extending from said transmitting station, and means including an automatic directive switch controllable byan attendant at said transmitting station for selectively connecting said monitoringtrunk to the output of any amplifying equipment in the syssaid trunk at the 0 an auxiliary ier station,

monitoring trunk extending between said stations, means to connect said monitoring trunk to the output side of said amplifying equipment, an indicator at said first station controllable over said monitoring trunk to indicate the'opera-tive condition of said amplifying equipment, and means to transmit a signal. over said monitoringtrunk to indicate failure of said amplifying equipment.

' 10. In a signaling system, a main transmission circuit extending between two stations, a receiving circuit connected thereto, a separate auxiliary monitoring circuit extending between said stations, means to connect-said auxiliary circuit to said main transmission circuit at one of said stations without interrupting the connection to said receiving circuit to permit an attendant to monitor from the other station, and means to enable attendants at both stations to converse over said monitoring circuit.

11. In a signaling system, a main transmission circuit extending between two stations, means to impress signaling currents upon said circuit at one station, amplifying equipment associated with said circuit at the other station, a receiving circuit connected thereto, an auxiliar monitoring circuit extending between sai stations, means to connect said auxiliary monitoring circuit to the output side of the amplifying equipment at said second station without interrupting the connecequipment associated with I tion' to said receiving circuit to enable an attendant to'monitor on the circuit from the equipment associatedwith each branch trunk at each outlying point, means for adjusting the amplification of said amplifying equipment at said central office, an auxiliary moni-' toring trunk extending from said transmitting station, a directively controlled switch,

12. In a signaling system, a main transmismeans for directively setting said switch at said transmitting station, and circuits controlled by said switch whereby in one setting it will connect said monitoring circuit to the.

output side of the amplifying equipment at said central office, whereby in other settings it will connect said monitoring circuit to the output side of the amplifying equipment associ ated with any one of said branch trunks at an outlying point, whereby in still other 'settings it will selectively control said means for adjusting the gain of the amplifying equipment at the central oflice, and whereby instill another setting it will connect an attendants telephone set at the central ofiice to said monitoring trunk to enable the attendant at said transmittingstation 'to converse with the attendant at the central oflice.

In testimony whereof I have signed my name to this specification this 29th day of I I July, 1924.

' JOHN F. TOOMEY. 

